Continuation session attribute

ABSTRACT

The present invention supports a new message format and protocol in an IP mobility system. Deallocation of a mobile node&#39;s IP address during a multipart communication session on a foreign network can cause serious communication and accounting errors. The new message format and protocol should eliminate the premature deallocation of a mobile node&#39;s IP address, which should reduce associated communication and accounting errors.

BACKGROUND OF THE INVENTION

[0001] Present-day Internet communications represent the synthesis oftechnical developments begun in the 1960s. During that time period, theDefense Department developed a communication system to supportcommunications between different United States military computernetworks, and later a similar system was used to support thecommunication between research computer networks at United Statesuniversities. These technological developments would subsequentlyrevolutionize the world by forming the basic elements of the Internet.

[0002] The Internet

[0003] The Internet, like so many other high tech developments, grewfrom research originally performed by the United States Department ofDefense. In the 1960s, Defense Department officials wanted to connectdifferent types of military computer networks. These different computernetworks could not communicate with each other because they useddifferent types of operating systems or networking protocols.

[0004] While the Defense Department officials wanted a system that wouldpermit communication between these different computer networks, theyrealized that a centralized interface system would be vulnerable tomissile attacks and sabotage. To avoid this vulnerability, the DefenseDepartment required that the interface system be decentralized with novulnerable failure points.

[0005] The Defense Department developed an interface protocol forcommunication between these different network computers. A few yearslater, the National Science Foundation (NSF) wanted to connect differenttypes of network computers located at research institutions across thecountry. The NSF adopted the Defense Department's interface protocol forcommunication between these research computer networks. Ultimately, thiscombination of research computer networks would form the foundation fortoday's Internet.

[0006] Internet Protocols

[0007] The Defense Department's interface protocol was called theInternet Protocol (IP) standard. The IP standard now supportscommunications between computers and networks on the Internet. The IPstandard identifies the types of services to be provided to users, andspecifies the mechanisms needed to support these services. The IPstandard also describes the upper and lower system interfaces, definesthe services to be provided on these interfaces, and outlines theexecution environment for services needed in the system.

[0008] One basic rule governing communications on the Internet is therequirement that a computer user does not need to get involved withdetails of each communication. In order to accomplish this goal, the IPstandard imposes a layered communications structure. All the layers arelocated on each computer in the network, and each module or layer is aseparate component that theoretically functions independent of the otherlayers.

[0009] Two types of transmission protocols may operate with the IPprotocol—the Transmission Control Protocol (TCP) or the User Datagramprotocol (UDP). TCP was developed to provide connection-oriented,end-to-end data transmission between packet-switched computer networks,and UDP supports a connection-less transmission between computernetworks. Unlike UDP, TCP provides certain error recovery anddata-checking services. The combination of TCP or UDP with the IPprotocol forms a suite of protocols for communication between computerson the Internet.

[0010] This suite of protocols form a standardized system for defininghow data should be processed, transmitted and received on the Internet.These protocols also define the network communication process, and moreimportantly, defines how a unit of data should look and what informationan information packet message should contain so that the receivingcomputer can receive the information message and interpret it properly.

[0011] Routing

[0012] Routers are used to regulate the flow of data through a computernetwork. A router interprets the logical address of an informationpacket, such as an IP address, and directs the information packet to itsintended destination. Information packets addressed between computers onthe same network are not allowed to pass outside the network, whileinformation packets addressed to a computer outside the network areallowed to pass to that computer on the outside network.

[0013] A routing table possesses sufficient information for a router tomake a determination on whether to accept the communicated informationpacket on behalf of a destination computer or pass the informationpacket onto another router on the network. The routing table alsopermits the router to determine where the information should beforwarded within the network. A Visitor Location Register (VLR) and HomeLocation Register (HLR) are two examples of such routers. A routingtable can be configured manually with routing table entries ordynamically according to changing network topologies—networkarchitecture, network structure, layout of routers, and interconnectionsbetween hosts and routers.

[0014] Authenticate, Authorize and Accounting (“AAA”)

[0015] In an IP-based mobile communications system, the mobilecommunication device (e.g. cellular phone, pager, etc.) can begenerically called a mobile node. Typically, a mobile node changes itspoint of attachment to the network while maintaining connectivity to itshome network. That is, a home network continues to transmit informationpackets to the mobile node even when the mobile node is located onanother network, sometimes referred to as a foreign network. While themobile node is coupled to the foreign network, the mobile node will beassigned an IP address for the transmission of information packets.

[0016] When a mobile node is operating on a foreign network, specializedservers must authenticate, authorize and collect accounting informationfor services rendered to the mobile node. This authentication,authorization, and accounting activity is called “AAA”, and AAA serverson the home and foreign network perform the AAA activities.

[0017] Authentication is the process of proving someone's claimedidentity, and security systems on a mobile IP network will often requireauthentication of the system user's identity before authorizing arequested activity. The AAA server authenticates the identity of anauthorized user, and authorizes the mobile node's requested activity.Additionally, the AAA server will also provide the accounting functionincluding tracking usage and charges for use of the network.

[0018] A mobile node is assigned an IP address while it conducts acommunication session on the foreign network. When a mobile node roamsthrough a foreign network, the wireless connection of the mobile node tothe foreign network may transition from one base station (or packetcontrol function) to another. When the transition of the wirelessconnection occurs, certain prior art protocols send accounting messagesto the AAA server that initiate the deallocation of the mobile node's IPaddress. This deallocation of the IP address may be unintentionalbecause the mobile node intends to continue its communication sessionwhile it roams the network. When the deallocation of the IP addressoccurs, information packets addressed to the mobile node may bemisdirected or lost. Other problems, such as billing and accountingdifficulties, may be encountered after a premature deallocation of theIP address.

SUMMARY OF THE INVENTION

[0019] When a mobile node's wireless connection transitions from onebase station (or packet control function) to another, the mobile nodemay want to maintain its connectivity to the network. This continuednetwork connection allows the mobile node to continue to transmit andreceive information packets in a multipart session. In order to preventthe premature deallocation of the mobile node's IP address in amultipart session, the present invention supports the use of a newmessage format and protocol for extending the time prior to adeallocation of the IP address. The new message format includes theaddition of an attribute to an accounting message that will cause theAAA server to recognize the mobile node's desire to maintainconnectivity to the network in a multipart session. In response to thenew message format attribute, a AAA server will not deallocate the IPaddress for the mobile node, and the same IP address can be used for themobile node after the transition of a wireless connection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The objects and features of the invention will become morereadily understood from the following detailed description and appendedclaims when read in conjunction with the accompanying drawings in whichlike numerals represent like elements and in which:

[0021]FIG. 1 is a schematic diagram of cellular sites on a mobile IPwireless communications network;

[0022]FIG. 2 is a schematic diagram of a mobile IP wirelesscommunications network;

[0023]FIG. 3 is a general format for a UDP datagram;

[0024]FIG. 4 is a general format for an attribute in a UDP datagram;

[0025]FIG. 5 is a step diagram for the authentication and accountingfunctions on a foreign network;

[0026]FIG. 6 is a new message format for an attribute to an AccountingStop.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In FIG. 1, cellular site 65 is shown in a mobile IP network. Incellular site 65, mobile node 64 is coupled to base station 69 viawireless connection 66. The base station 69 is coupled to the basestation controller 75 via connections 70 and 71. Cellular site 68 has abase station 73 to support wireless connections in that cellular site.Base station 73 is coupled to the base station controller 75 viaconnections 72 and 71. Cellular site 67 has a base station 74 to supportwireless connections in that cellular site. Base station 74 is coupledto the base station controller 75 via connections 75 and 71.

[0028] The base station controller 75 is coupled to a foreign network 40via communication line 76. The foreign network 40 is coupled to theInternet 36 via communication line 39. The terms base station or basestation controller can be referred to as a base station transceiver,packet control function or base station subsystem. The term foreignnetwork can be referred to as visited network.

[0029] When operating within cellular site 65, the mobile node 64communicates through a wireless connection 66 to base station 69. Themobile node communicates with the Internet 36 through the base stationcontroller 75 and the foreign network 40. When communicating on theforeign network 40, the mobile node 64 is assigned a specific IPaddress. The mobile node 64, however, may roam around the wirelessnetwork shown in FIG. 1. In so doing, the mobile node 64 may leave thecellular site 65 and enter the cellular site 68. When such movementoccurs, the wireless connection 66 will terminate, and a new wirelessconnection between mobile node 64 and base station 73 will be initiated.This movement and the reconnection on the wireless network is called awireless transition.

[0030] After a wireless transition occurs, the AAA servers in theforeign network 40 will receive control messages that will cause thedeallocation of the IP address assigned to the mobile node 64. Themobile node 64, however, will need to maintain the same IP address if itwants to maintain consistent connectivity with the outside networks onthe Internet 36. If a deallocation of the IP address occurs, informationpackets addressed to the mobile node 64 may be lost or misdirected.Further, accounting errors may occur based upon the deallocation andreallocation of the former IP address to another mobile node. Thepresent invention solves the premature deallocation problem with a newmessage format and protocol for use with AAA servers.

[0031]FIG. 2 shows a diagram of a wireless IP mobility network havingthe mobile node 64, a foreign network 40, a home network 10, and theInternet 35. The mobile node 64 is linked to a radio network (RN) 60 bya wireless communication link 66. The RN 60 is linked to the foreignnetwork 40 via communication link 62, sometimes called the R-Pinterface. The foreign network 40 has a foreign agent, also referred toas a Packet Data Serving Node (PDSN) 58.

[0032] PDSN 58 is coupled to RN 60 via communication link 62. PDSN 58 iscoupled to a foreign network buss line 50 by communication link 54. Theforeign network 40 includes a AAA server, also referred to as a RADIUSserver 47, which is coupled to buss line 50 via communication link 52.The foreign network 40 is coupled to the Internet 35 by communicationlink 37.

[0033] The home network 10 is coupled to the Internet 35 bycommunication link 30. The home network 10 has a central buss line 20that is coupled to communication link 30. Home network 10 has a AAAserver 27 coupled to buss line 20 by communication link 26. Home agent28 is linked to the central buss line 20 by communication link 24.

[0034] The communication protocol used by the IP mobility system shownon FIGS. 1 and 2 uses a User Datagram Protocol (“UDP”) with the IPstandard. As shown in FIG. 3, a standard UDP datagram for an accountingmessage format 100 is used in the present invention, and message 100includes a code field 110 of one byte in length. The code 110 identifiesthe type of RADIUS packet as an accounting message, either request orresponse. For an Accounting Request message the code 110 will have avalue of 4, and for an Accounting Response message the code 110 willhave a value of 5.

[0035] The accounting message format 100 also has an identifier datafield 120 of one byte in length. The identifier data 120 is used toassist with the identification of corresponding accounting requests andresponses. The accounting message format has a length field 130 of twobytes in length to indicate the length of the entire accounting message100 including the code 110, identifier 120, length 130, authenticator140, and all attribute fields 150.

[0036] The message format 100 includes an authenticator field 140 thatis 16 bytes in length. The authenticator field 140 is used toauthenticate the message between the PDSN 58 and the AAA RADIUS server47. The attribute field 150 of accounting message 100 is variable inlength and contains messages involved with the authentication,authorization, and accounting operations for the mobile node's 64connectivity to foreign network 40 and other networks.

[0037] In message format 100, the format for the attribute field 150 isshown in FIG. 4. The three data structures in the attribute field 150include the type field 210 (designated by “T”) which occupies the first8 bits of the attribute field 150, the length field 220 (designated by“L”) which occupies the next 8 bits of the attribute field 150, and thedata field 230 (designated by “D”) which occupies the remaining bits inthe attribute field 150. The type field 210 indicates the particulartype of attribute in the attribute field 150, and the length field 220indicates the length in bytes of the attribute field 150. The data field230 may be zero or more bytes in length, and sets forth the applicabledata that is being transmitted.

[0038] In a communication session involving the mobile node 64 on theforeign network 40, the mobile node 64 initiates a packet data sessionby contacting the RN 60 over communication link 66. The RN 60 in turnestablishes communication with PDSN 58 over communication link 62. Asshown in FIG. 5, the first communication from the mobile node 64 to thePDSN 58 is a Link Control protocol negotiation message at step 405. Thenegotiation message at step 405 establishes an R-P Interface 62 betweenthe PDSN 58 and the RN 60.

[0039] After the contact is established between the mobile node 64 andthe PDSN 58, it is necessary to authenticate the identity of the mobilenode 64. The mobile node 64 sends an authentication message with auser-name to the PDSN 58 at step 410. The PDSN 58 then sends an AccessRequest message with the user name to the RADIUS server 47 at step 415.The Access Request message at step 415 contains information about themobile node 64 including information such as a user password,destination port, client ID. Other information may be provided in theAccess Request message.

[0040] The RADIUS server 47 processes the information in the AccessRequest message to determine if the mobile node 64 is authorized toaccess the network 40. If the mobile node 64 is authorized, the RADIUSserver 47 generates an Access Accept message. The Access Accept messageis transmitted to the PDSN 58 at step 420.

[0041] The RADIUS server 47 maintains a pool of dynamic IP addresses forassignment to mobile nodes on the foreign network 40. The IP addressesare used to route information packets to the Mobile Node 64 andaccomplish AAA functions. This pooling of IP addresses is managed at theRADIUS server 47. This allocation of an IP address by the RADIUS server47 occurs when the Access Accept message is generated and sent to thePDSN 58 at step 420. The PDSN 58 will use the IP address to locate themobile node 64 on the RN 60 and direct information packets to theappropriate base stations on the RN 60 for communication with the mobilenode 64.

[0042] In response to the Access Accept message, the PDSN 58 generatesan Authentication End message that is transmitted to the Mobile Node 64at step 425. If the mobile node 64 is not authorized by the RADIUSserver 47, an Access Reject message is transmitted to the PDSN 58 toterminate the attempted communication with the mobile node 64.

[0043] Once the Mobile Node 64 is successfully linked to the homenetwork 10 and the data packet communication session can begin, theRADIUS server 47 will begin accounting for the mobile node's usage ofthe foreign network 40 resources. The mobile node 64 sends an initialaccounting message IPCP to the PDSN 58 at step 430. The PDSN 58 respondsto the mobile node 64 with a response at step 435. The PDSN 58 willgenerate and transmit an Accounting Start message to the RADIUS server47 to start the accounting functions. The PDSN 58 transmits theAccounting Start message to the RADIUS server 47 at step 440.

[0044] This will complete the setup for the accounting process for thepacket data communication session. The remaining communication sessiontasks and linkages are accomplished by the PDSN 58 establishing aconnection over the Internet 35 with the Home Network 10. Thecommunication session takes place at step 445 by the interactionsbetween the mobile node 64 and the PDSN 58, and any other networks.

[0045] At the end of the communication session, the PDSN 58 is notifiedof the communication termination and transmits an Accounting Stopmessage from the PDSN 58 to the RADIUS server 47. The Accounting Stopmessage is transmitted at step 450. In response to the Accounting Stopmessage at step 450, the mobile node's IP Address is deallocated backinto the pool for subsequent allocation to another mobile node.

[0046] A problem can arise when certain mobility events occur, such asthe handoff of control over the mobile node's wireless communicationfrom one base station to another. When such a mobility event occurs, thePDSN 58 may transmit an Accounting Stop message to the RADIUS server 47at step 450 followed by an Accounting Start message to the RADIUS serverat step 455. The combination of the Accounting Stop message at step 450and the Accounting Start message at step 455 is meant to indicate thatthe mobile user is continuing the communication in a multipartcommunication session.

[0047] As part of a multipart communication session, the mobile node'sIP address should not be deallocated. The RADIUS server 47, however, maystill deallocate the mobile node's IP address in response to theAccounting Stop message at step 450 before it has an opportunity toconsider the Accounting Start message at step 455. Such a deallocationcould cause an erroneous assignment of the same IP address to anothermobile node. This erroneous assignment could disrupt propercommunications and the accounting function for the mobile node.

[0048] The present invention solves the premature deallocation problemby attaching a new message attribute 150 to the Accounting Stop messagetransmitted to the RADIUS server 47 at step 450. The new attribute 150is called a Continuation Session Attribute, and its format is shown at500 in FIG. 6. The type field 510 in Continuation Session Attribute 500is assigned a value of 26 for Vendor-Specific for all attributes. TheLength field 520 in attribute 500 is the length of all the data fields(in bytes) in the attribute.

[0049] The Vendor-ID field 530 is the same for all attributes, and inthis context, the Vendor-ID is assigned a value of 5535. This Vendor-IDfield also occupies the field 531 of attribute 500. The Vendor-Typefield 535 specifies the vendor specific type of attribute and is 8 bitsin length. The Vendor-Length field 540 is the length in bytes of thevendor identification fields. An Accounting Stop message with thisSession Continue Attribute and the following Accounting Start messagemust have the same ID value in the Identifier field.

[0050] When an Accounting Stop message is received by the RADIUS server47 at step 450, the Continuation Session Attribute 500 attached theretowill indicate to the RADIUS server 47 that the Accounting Stop messageis not the end of the communication session, but the Accounting Stopmessage will be followed by an Accounting Start message that willcontinue the communication session. This attribute 500 will instruct theRADIUS server 47 not to deallocate the mobile node's IP address, and assuch, the multipart communication session will not be erroneouslyinterrupted by a premature deallocation of the IP address. When theAccounting Start message containing the correlating Identifier is thenreceived by the RADIUS server 47, the accounting process for thecommunication session of mobile node 64 will continue withoutinterruption or error.

[0051] While the invention has been particularly shown and describedwith respect to preferred embodiments, it will be readily understoodthat minor changes in the details of the invention may be made withoutdeparting from the spirit of the invention. Having described theinvention, we claim:

1. A communications system, comprising: a radio network coupled to a serving computer on a first network; a mobile node coupled to the radio network by a wireless communication link; a communication server computer linked to the serving computer, said communication server computer controlling the allocation of addresses for the mobile node and performing accounting functions for the first network, and; a control message transmission on the first network comprising a data element that denotes the continuation of the mobile node's communication session on the first network.
 2. The communications system in claim 1 wherein the control message includes a type field.
 3. The communications system in claim 1 wherein the control message includes a length field.
 4. The communications system in claim 1 wherein the control message includes a vendor-type field.
 5. The communications system in claim 1 wherein the control message includes a field containing the data element.
 6. The communications system in claim 1 wherein the serving computer is coupled to an Internet.
 7. The communications system in claim 1 wherein the serving computer is coupled to a second network.
 8. The communication system in claim 1 wherein the communication server computer will not change the mobile node's address on the foreign network after receiving the control message.
 9. The method of continuing a communication session on a communication system comprising the steps of: transmitting a request message from a serving computer to a first serving computer, said request message contains a session continuation message; and receiving the request message from said serving computer and maintaining an address allocation for a mobile node on the foreign network.
 10. The method of continuing a communication session in claim 9 wherein the session continuation message is a data element in an accounting message.
 11. The method of continuing a communication session in claim 9 wherein the server computer continues accounting functions for an ongoing communication session in response to the request message.
 12. The method of continuing a communication session in claim 9 wherein the session continuation message includes a type data element.
 13. The method of continuing a communication session in claim 9 wherein the session continuation message includes a length data element.
 14. The method of continuing a communication session in claim 9 wherein the session continuation message includes a vendor-type data element.
 15. The method of continuing a communication session in claim 9 wherein the session continuation message includes an identifier data element.
 16. The method of continuing a communication session in claim 9 wherein the session continuation message includes a session continuation attribute data element.
 17. The method of continuing a communication session in claim 16 wherein the session continuation attribute is a data value in an accounting message.
 18. A method for supporting communications on packet-based network comprising the steps of: receiving a continuation session message, and, continuing an accounting function a mobile node address on an ongoing communication session after receipt of the continuation session message.
 19. The method for supporting communications of claim 18 wherein the continuation session message includes a type data element.
 20. The method for supporting communications of claim 18 wherein the continuation session message includes a length data element.
 21. The method for supporting communications of claim 18 wherein the continuation session message includes a vendor-type data element.
 22. The method for supporting communications of claim 18 wherein the continuation session message includes an identifier data element.
 23. The method for supporting communications of claim 18 wherein the continuation session message includes a session continuation attribute data element. 